Dense Bi1.5-xY0.5CuxO3-delta membranes in fluorite phase (delta phase) with different CuO concentration (x = 0.005-0.015) and thickness (1-3 mm) were prepared from corresponding powders synthesized by the citrate method. Oxygen permeation through these membranes was studied using a high-temperature permeation system to examine the oxygen transport mechanism of the membranes. The oxygen permeation fluxes through these membranes (2 mm thick) at 800 degrees C are in the range (5.0-9.2) x 10(-9) mol/cm(2) s at P’(O2) of 0.21 atm and P "(O2) of 5 x 10(-4)-1 x 10(-3) atm. The permeation flux is inversely proportional to the membrane thickness, indicating bulk diffusion being the rate-limiting step. The driving force for the oxygen permeation through the membranes is (P "(-1/4)(O2)-P’(-1/4)(O2)). The activation energy for oxygen permeation is 136, 113 and 80 kJ/mol for the membranes with 0.25, 0.5, and 0.75 mol% CuO concentration, respectively.